NHTSA initiated this rulemaking with the publication of a Notice of Proposed
Rulemaking (NPRM)(66 FR 38982, Docket No. NHTSA-2000-8572) on July 26, 2001. The
NPRM proposed to require passenger cars, light trucks, multipurpose passenger vehicles, and
buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual
wheels on an axle, to be equipped with a tire pressure monitoring system (TPMS).

The agency sought comment on two alternative sets of performance requirements for
TPMSs and proposed adopting one of them in the final rule. The first alternative would have
required that the driver be warned when the pressure in any single tire or in each tire in any
combination of tires, up to a total of four tires, had fallen to 20 percent or more below the vehicle
manufacturer's recommended cold inflation pressure for the vehicle's tires (the placard
pressure), or a minimum level of pressure specified in the standard, whichever was higher. (This
alternative is referred to below as the four-tire, 20 percent alternative.) The second alternative
would have required that the driver be warned when the pressure in any single tire or in each tire
in any combination of tires, up to a total of three tires, had fallen to 25 percent or more below the
placard pressure, or a minimum level of pressure specified in the standard, whichever was higher.
(This alternative is referred to below as the three-tire, 25 percent alternative.) The minimum
levels of pressure were the same in both proposed alternatives. The adoption of four-tire, 20
percent alternative would have required that drivers be warned of under-inflation sooner and in a
greater array of circumstances. It would also have narrowed the range of technologies that
manufacturers could use to comply with the new standard.

There are two types of TPMSs currently available, direct TPMSs and indirect TPMSs.
Direct TPMSs have a tire pressure sensor in each tire. The sensors transmit pressure information
to a receiver. Indirect TPMSs do not have tire pressure sensors. Current indirect TPMSs rely on
the wheel speed sensors in an anti-lock braking system (ABS) to detect and compare differences
in the rotational speed of a vehicle's wheels. Those differences correlate to differences in tire
pressure because decreases in tire pressure cause decreases in tire diameter that, in turn, cause
increases in wheel speed.

To meet the four-tire, 20 percent alternative, vehicle manufacturers likely would have had
to use direct TPMSs because even improved indirect systems would not likely be able to detect
loss of pressure until pressure has fallen 25 percent and could not detect all combinations of
significantly under-inflated tires. To meet the three-tire, 25 percent alternative, vehicle
manufacturers would have been able to install either direct TPMSs or improved indirect TPMSs,
but not current indirect TPMSs.

B. Highlights of the Preliminary Determination About the Final Rule

NHTSA preliminarily determined to issue a final rule that would have specified a four-year
phase-in schedule (1) and allowed compliance with either of two options
during the phase-in, i.e., between November 1, 2003 and October 31, 2006. Under the first option, a vehicle's
TPMS would have had to warn the driver when the pressure in one or more of the vehicle's
tires, up to a total of four tires, was 25 percent or more below the placard pressure, or a minimum
level of pressure specified in the standard, whichever pressure was higher. (This option is
referred to below as the four-tire, 25 percent option.) Under the second option, a vehicle's
TPMS would have had to warn the driver when the pressure in any one of the vehicle's tires was
30 percent or more below the placard pressure, or a minimum level of pressure specified in the
standard, whichever pressure was higher. (This option is referred to below as the one-tire, 30
percent option.) The minimum levels of pressure specified in the standard were the same for
both compliance options.

After the phase-in, i.e., after October 31, 2006, the second option would have been
terminated, and the provisions of the first option would have become mandatory for all new
vehicles. Thus, all vehicles would have been required to meet a four-tire, 25 percent
requirement.

C. OMB Return Letter

After reviewing the draft final rule, OMB returned it to NHTSA for reconsideration, with
a letter explaining its reasons for doing so, on February 12, 2002. In the letter, OMB stated its
belief that the draft final rule and accompanying regulatory impact analysis did not adequately
demonstrate that the agency had selected the best available method of improving overall vehicle
safety.

D. Highlights of the Final Rule

In response to the OMB return letter, the agency has decided to divide the final rule into
two parts. The first part is contained in this document, which establishes requirements for
vehicles manufactured during the first three years, i.e., between November 1, 2003, and October
31, 2006, and phases them in by increasing percentages of production. The second part will
establish requirements for vehicles manufactured on or after November 1, 2006.

The agency has divided the final rule into two parts because it has decided to defer its
decision as to which long-term performance requirements for TPMS would best satisfy the
mandate of the TREAD Act. This deferral will allow the agency's consideration of additional
data on the effect and performance of TPMSs. From the beginning, the agency has sought to
comply with the mandate and safety goals of the TREAD Act in a way that encourages
innovation and allows a range of technologies to the extent consistent with providing drivers with
sufficient warning of low tire pressure under a broad variety of the reasonably foreseeable
circumstances in which tires become under-inflated.

1. Part One -- Phase-in (November 2003 through October 2006)

NHTSA has decided to require vehicle manufacturers to equip their light vehicles (i.e.,
those with a gross vehicle weight rating (GVWR) of 10,000 lbs. or less) with TPMSs and to give
them the option for complying with either of two sets of performance requirements during the
period covered by the first part of the final rule, i.e., from November 1, 2003 to October 31,
2006. The options are the same as those in the preliminary determination about the final rule.

Under the first set or compliance option, the vehicle's TPMS will be required to warn the
driver when the pressure in any single tire or in each tire in any combination of tires, up to a total
of four tires, is 25 percent or more below the vehicle manufacturer's recommended cold
inflation pressure for the tires, or a minimum level of pressure specified in the standard,
whichever pressure is higher. Under the second compliance option, the vehicle's TPMS will be
required to warn the driver when the pressure in any single tire is 30 percent or more below the
vehicle manufacturer's recommended cold inflation pressure for the tires, or a minimum level of
pressure specified in the standard, whichever pressure is higher. (2)

The two compliance options are outgrowths of the alternative sets of requirements
proposed in the NPRM. In response to comments confirming that current indirect TPMSs cannot
meet the proposed three-tire, 25 percent under-inflation requirements, and in order to allow those
systems to be used during the phase-in, the agency is adopting requirements for detection of one-tire,
30 percent under-inflation as the first option. For the second option, the agency is adopting
requirements for detection of 4-tire, 25 percent under-inflation. Adopting those requirements,
instead of the proposed requirements for four-tire, 20 percent under-inflation, will permit
manufacturers to use either direct TPMSs or hybrid TPMSs, i.e., TPMSs that combine direct and
indirect TPMS technologies. One TPMS supplier indicated the potential for developing and
producing hybrid systems, although it also indicated that it did not currently have plans for doing
so. The agency believes that the difference in benefits between TPMSs meeting four-tire, 20
percent requirements and TPMSs meeting four-tire, 25 percent requirements should not be
substantial.

To facilitate compliance with the options, the rule phases them in by increasing
percentages of production. Ten percent of a vehicle manufacturer's light vehicles will be
required to comply with either compliance option during the first year (November 1, 2003 to
October 31, 2004), 35 percent during the second year (November 1, 2004 to October 31, 2005),
and 65 percent during the third year (November 1, 2005 to October 31, 2006). These percentages
are the same as those in the preliminary determination about the final rule. The agency is
allowing carry-forward credits for vehicles that are manufactured during the phase-in and are
equipped with TPMSs that comply with the four-tire, 25 percent option. It is not allowing credits
for TPMSs complying with the other option for the same reason that the agency is requiring
manufacturers to provide consumers with information about the performance limitations of those
systems.

The combination of the two compliance options and the phase-in will allow
manufacturers to continue to use current indirect TPMSs during that period and ease the
implementation of the TPMS standard. The agency notes that, for vehicles already equipped
with ABS, the installation of a current indirect TPMS is the least expensive way of complying
with a TPMS standard. The compliance options and phase-in will also give manufacturers the
flexibility needed to innovate and improve the performance of their TPMSs. This flexibility will
improve the chances that ways can be found to improve the detection of under-inflation as well
as reduce the costs of doing so.

The owner's manual for vehicles certified to either compliance option will be required to
include written information explaining the purpose of the low tire pressure warning telltale, the
potential consequences of driving on significantly under-inflated tires, the meaning of the telltale
when it is illuminated, and the actions that drivers should take when the telltale is illuminated. In
addition, the owner's manual in vehicles certified to the one-tire, 30 percent option will be
required to include information on the inherent performance limitations of current indirect
TPMSs because the agency anticipates that most indirect TPMSs installed to comply with that
option will exhibit those limitations and because a vehicle owner survey indicates that a
significant majority of drivers would be less concerned, to either a great extent or a very great
extent, with routinely maintaining the pressure of their tires if their vehicle were equipped with a
TPMS. Under both compliance options, the TPMS will be required to have a low tire pressure-warning telltale (yellow).

2. Part Two -- November 2006 and Thereafter

Beginning November 1, 2006, all passenger cars and light trucks, multipurpose passenger
vehicles, and buses under 10,000 pounds GVWR will be required to comply with the
requirements in the second part of this final rule. The agency will publish the second part of this
final rule by March 1, 2005, in order to give manufacturers sufficient lead time before vehicles
must meet the requirements.

In anticipation of making the decision in part two of this final rule about the long-term
requirements, the agency will leave the rulemaking docket open for the submission of new data
and analyses. The agency also will conduct a study comparing the tire pressures of vehicles
without any TPMS to the pressures of vehicles with TPMSs that do not comply with the four-tire,
25 percent compliance option. When completed, it will be placed in the docket for public
examination. After consideration of the record compiled to this date, as supplemented by the
results of the tire pressure study and any other new information submitted to the agency, NHTSA
will issue the second part of this rule by March 1, 2005.

Based on the record now before the agency, NHTSA tentatively believes that the four-tire,
25 percent option would best meet the mandate in the TREAD Act. However, it is possible
that the agency may obtain or receive new information that is sufficient to justify a continuation
of the compliance options established by the first part of this final rule, or the adoption of some
other alternative.

E. Summary Comparison of the Preliminary Determination and the Final Rule

The primary difference between the preliminary determination and the final rule is one of
timing, instead of substance. The options and percentages of production for the phase-in years
are unchanged. (3) The final rule does differ from the preliminary
determination in the timing of the agency's decision about the performance requirements for the years
following the phase-in period.

Summary Comparison of the Preliminary Determination and the Final Rule

Preliminary Determination

Final Rule

Application

Passenger cars, trucks, multipurpose passenger vehicles, and buses with a
GVWR of 10,000 pounds or less, except those vehicles with dual wheels on an axle

Same

Short-term (11/1/03 - 10/31/06)

Compliance Options

Option 1: TPMS must warn the driver when the pressure in any single tire or
in each tire in any combination of tires, up to a total of four tires, has fallen to 25 percent
or more below the vehicle manufacturer's recommended cold inflation pressure for the
tires, or a minimum level of pressure specified in the standard, whichever pressure is
higher.Option 2: TPMS must warn the driver when the pressure in any single tire has fallen to
30 percent or more below the vehicle manufacturer's recommended cold inflation
pressure for the tires, or a minimum level of pressure specified in the standard, whichever
pressure is higher. Same

Same

Same

Phase-inSchedule

10% of a vehicle manufacturer's light vehicles will be required to comply
with either compliance option during the first year (November 1, 2003 to October 31,
2004), 35 percent during the second year (November 1, 2004 to October 31, 2005), and 65
percent during the third year (November 1, 2005 to October 31, 2006).

Same

Long-term(11/1/06 & thereafter)

PerformanceRequirements

TPMS must warn the driver when the pressure in any single tire or in
each tire in any combination of tires, up to a total of four tires, has fallen to 25 percent or
more below the vehicle manufacturer's recommended cold inflation pressure for the tires,
or a minimum level of pressure specified in the standard, whichever pressure is higher.

Decision to be made by March 1, 2005

1 The phase-in schedule was as follows: 10 percent of a manufacturer's affected vehicles would
have had to comply with either compliance option in the first year; 35 percent in the second year; and 65
percent in the third year. In the fourth year, 100 percent of a manufacturer's affected vehicles would
have had to comply with the long-term requirements, i.e., the four-tire, 25 percent compliance option.

2 The minimum levels of pressure are the same for both compliance options.

3 The final rule does require that additional information be placed in the vehicle's owner manual.